Western blot analysis of tyrosine phosphorylation (pY) in protein extracts of VAS, TES and sperm. (A) SDS-PAGE of total protein extracts of VAS, TES and sperm. Asterisks point to the MSPs that exist exclusively in sperm. (B) Western blot analysis of VAS, TES and sperm protein extracts probed with anti-pY. Arrows indicate a ~45 KD protein that is abundant in sperm extracts (S100).